Results from studies of coaggregation among oral bacteria during the past few years have built a firm foundation for future work. Bacteria isolated from subgingival and supragingival plaque have been examined and show to exhibit a highly specific and ordered set of cell-to-cell interactions that forms a network of intergeneric cell surface recognitions. These cellular recognitions likely play a major role in the onset and development of bacterial plaque during the progressive changes in bacterial populations accompanying periodontal disease. We took advantage of this information to develop an in vitro model system of multiple cell-type coaggregations which simulates dental plaque. Several principles of coaggregation were predicted and demonstrable which give credence to the simulated plaque model. Results from related studies indicated that the oral bacteroides are particularly suited to be coaggregation bridge organisms because they are one of a few bacteria that recognize both oral streptococci or oral actinomyces and Actinomyces israelii. They also are able to be effective competitors against other bacteria for lactose-sensitive coaggregations with oral streptococci. Coaggregation-defective mutants and bacteriophage-resistant mutants have been used as tools to unravel a sialic acid-inhibitable coaggregation that was complicated by being masked by other kinds of coaggregation mechanisms. The efforts of each of these investigative approaches and their results are focused on understanding the relationship of cell surface recognitions among oral bacteria and their role in microbial ecology.